The present invention generally pertains to the storage of energy and the retrieval thereof as heat, and is specifically directed to physical-chemical methods and systems for storing and retrieving heat.
There is a need for an improvement in storing energy. Most forms of energy are readily converted to heat and may be stored by heating a storage medium. The storage medium may be an inert substance, such as water or rocks, wherein the heat is stored by raising the temperature of the substance and retrieved by moving a relatively cooler heat transfer fluid over the surface of the storage medium. Heat storage by raising the temperature of chemically inert material has the disadvantage of requiring thermal insulation to prevent heat loss and requiring a large volume of substance to store useful quantities of heat.
Heat also may be stored by reversible physiochemical reactions. In one such system, a salt hydrate is heated in a container to above its latent heat of fusion to its liquid state to store the heat. The heat is retrieved by passing a relatively cooler heat transfer fluid such as air or water around the salt hydrate container, thereby producing an exothermic crystallization process, whereby heat is surrendered to the heat transfer fluid. One difficulty with this system is that a stratification layer of the crystalized salt tends to form at the heat transfer surface thereby creating a barrier which reduces the rate of heat transfer.